Structural studies of E. coli polyribosomes and ribosomal subunits have shown that these macromolecules may exist in several forms. The structural differences are detected by the high-resolution technique of polyacrylamide gel electrophoresis. Amino acid starvation or treatment of cells with specific antibiotics produces an alteration in the polyribosomes which is reflected in an increased electrophoretic mobility in the gels. In addition, under normal conditions, two forms of the 30s subunit exist which are related to specific stages in the ribosome cycle. I shall investigate the compositional and configurational changes in polyribosomes with altered structures produced both in vivo and in vitro. I am attempting to examine by electron microscopy these particles after they are separated in the gels by electrophoresis. In addition I shall isolate and characterize the two forms of the 30s subunit and correlate their structure with particular steps in protein synthesis. Finally I propose to isolate various precursor intermediates of ribosome subunits by the technique of gel electrophoresis to learn more about the order of assembly in vivo.